Inverse micelles water pool

Hydrated electron probe inverse micelles. Hydrated electrons (e aq) are expected to be a very good probe to test the water pool of reverse micelles. The physical properties of hydrated electrons obtained by pulse radiolysis in AOT reverse micelles were experimentally determined (Calvo-Perezet al., 1981 Pileni,... 

An inverse (or reverse) micelle, which forms in a non-polar solvent, will have the hydrophilic head groups oriented toward the inside of the sphere, where a water pool is formed and a hydrophilic probe can become associated [10]. Some surfactants commonly employed to stabilize reverse micelles include sodium diisooctylsulfosuccinate (AOT), benzylhexadecyldimethylammonium chloride (BHDC), and dodecylammonium propionate (DAP). Ionic surfactants induce formation of a larger water pool than non-ionic surfactants, but the size of the hydrophilic core also depends on temperature and on the ratio of water to surfactant. 

The kinetic complexity seen in oriented micelles persists in inverse micelles. The distribution of electron transfer quenchers within the water pool follows Poisson statistics and enables the kinetic data to describe migration rates to and from the aqueous subphase [65]. These orientation effects also make possible topological control of non-electron transfer photoreactions occurring within AOT micelles [66]. 

Figure 3.14 Inverted AOTmicelles dispersed in isooctane dissolve enzymes in the central water volume (inverse micelles). Polar substrates are enzymatically converted to less polar products. They are re-ejected into the apolar isooctane medium the enzyme in the water pool can take up more substrate. ...

At intermediate concentrations considerably above the CMC, rod-shaped micelles often form. At very high concentrations, lamellar aggregates and other condensed phases form. In organic solvents, some surfactants form spherical inverse micelles with the head groups facing small pools of trapped water, with hydrocarbon tails facing the bulk solvent phase (Fig. 2). 

In contrast to emulsions, which are unstable macrodisperse systems (1-10 pm in droplet diameter), microemulsions are homogeneous, optically transparent, thermodynamically stable systems that can be formed only in specific ranges of temperature, pressure, and composition. They consist of droplets of water tens of nanometers in size dispersed within an immiscible organic (oil) phase [inverse micelles, or water-in-oil (W/0) microemulsions] or vice versa, oil pools dispersed within an aqueous phase [direct micelles, or oil-in water (OAV) microemulsions]. The droplets are encased in a surfactant shell as in emulsions or, more frequently, in a shell consisting of a suitable surfactant and a cosurfactant (usually an alcohol) and are thus stabilized. 

Reverse micelles formed in water-in-oil (w/o) microemulsions, structurally inverse analogues to normal micelles, are capable of hosting proteins/enzymes in their so-called water pool. The biomolecule can be entrapped in the water pools, avoiding direct contact with the organic solvent, potentially limiting their... 

The hydrolysis of carbohydrates in dodecylbenzene sulphonic acid in dioxane-water mixtures has been the subject of one study in which it Was found that the hydrolysis was accelerated by about 21 times in dioxane mixtures above 60% by volume [126], but no coherent mechanism was put forward for the catalysis. Non-ionic surfactants may form inverse micelles in non-aqueous solvents in the presence of small amounts of water. Triton X-1(X), for example, micellizes in carbon tetrachloride on addition of water. This system, which obviously does not suffer the problems which result from the dissociation of the head groups of ionic surfactants in the water pool, has been used to investigate the hydration reaction of acetaldehyde [127]. This acid-catalysed reaction is increased by a factor of 10000 over that in water (Table 11.9). In spite of the nonionic nature of the peripheral head groups surrounding and penetrating the aqueous core, the nature of the water is such that ionization of solubilized species is changed. 

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